The present invention relates to active attenuation of vibration, that is to say the operation which consists in attenuating certain types of vibration by superimposing other vibration created in phase opposition with the vibration to be attenuated.
It applies to the active attenuation of any vibration, and more particularly to acoustic, mechanical or similar vibration.
The technique of active attenuation by feedback is already known, based on a feedback loop configured to generate active attenuation on a framework which is subject to the vibration.
The feedback loop comprises an input linked to vibration sensor means known as the xe2x80x9cnearxe2x80x9d means, which are arranged on the framework, and an output linked to vibration actuator means which are arranged on the framework, in proximity to the near sensor means. The signal measured by the near sensor means is injected directly into the actuator means via filtering means which correct said signal in order to attempt to cancel out its energy.
This feedback technique makes it possible to obtain vibration attenuation with a certain amount of gain, without generating instability in a band of processing frequencies. This processing band most often corresponds to low frequencies, for example, in terms of acoustic vibration, to the frequency band going from 0 to 600 Hz.
However, this feedback technique generates instability at high frequencies. It is therefore not totally satisfactory for obtaining vibration attenuation in a wide frequency band.
The technique of active feedforward attenuation is also known, in which reference vibration, upstream of the propagation of the vibration, and which are destined to propagate in the medium to be treated, are detected by sensor means known as xe2x80x9cremotexe2x80x9d means, then processed by filtering means so as to determine the command to be applied to the actuator means.
The feedforward technique is centered on adaptive-type filtering means with coefficients adapted in real time according to an algorithm chosen to minimize the energy of the vibration picked up by the near sensor means as a function of the energy of the reference vibration picked up by the remote sensor means.
Such a feedforward technique is generally satisfactory in dealing with vibration in a narrow frequency band. In contrast, when vibration has to be attenuated in a wide frequency band, lengthy and expensive adaptive filtering is generally required.
One solution for shortening the convergence time of the feedforward filtering algorithm is described in the MIYASAKI et al. document, 1994, xe2x80x9cConsideration about Feed back, Feed forward, Hybrid Control for Active Control of Micro-Vibrationxe2x80x9d, Second International Conference on Motion on Vibration Control, Yokohama, Aug. 30-Sep. 3, 1994. This consists in juxtaposing feedback-type active damping and feedforward filtering. The active feedback damping first of all applies damping of the vibration at a given frequency, generally the fundamental vibration frequency of the framework. Next, the feedforward filtering applies its attenuation to thus pre-damped vibration, which makes it possible to compress the impulse response of the actuator means/near sensor means secondary paths and thus shortens the processing of the feedforward filtering.
However, the active feedback damping is applied here at a single frequency, which renders this solution inappropriate and ineffective for an active treatment over a wide frequency band. This active damping is in fact equivalent to a passive damping since it treats only the fundamental frequency of the framework, which is completely different from wideband active control by feedback filtering. Moreover, it is a question here of simple juxtaposition of feedforward filtering and of active damping in which no synergy of the techniques is introduced.
The present invention affords a solution to these problems.
It first of all envisages providing active attenuation of the vibration in a wide frequency band.
Another aim of the invention is to provide active attenuation of xe2x80x9chybridxe2x80x9d type in which feedforward filtering is grafted onto feedback filtering or vice versa, so as to enhance the respective behavior of said feedforward and feedback filtering with a resultant attenuation greater than the algebraic sum of the attenuation by said filtering types taken separately.
The present invention relates to an active vibration attenuation device of the type comprising:
a framework likely to be subject to vibration to be attenuated;
first vibration sensor means, arranged on the framework in a first predetermined geometric relationship with respect to said framework;
vibration actuator means, arranged on the framework in proximity to the first sensor means; and
filtering means comprising at least an input linked to the first sensor means and an output linked to the actuator means, the filtering means being configured to generate active attenuation of the vibration on the framework;
second vibration sensor means, arranged on the framework in a second predetermined geometric relationship with respect to said framework;
summation means possessing a first input, a second input, and an output linked to the actuator means.
According to a general definition of the invention, the filtering means comprise:
nonadaptive-type feedback filtering means possessing an input linked to the first sensor means and an output linked to the first input of the summation means, and suitable for generating nonadaptive active attenuation of the vibration on the framework, without generating instability in a first frequency band;
measurement means suitable for measuring, in advance, in the presence of the feedback filtering means, the transfer function between the actuator means and the first sensor means;
adaptive-type feedforward filtering means comprising a first input linked to the second sensor means, a second input linked to the first sensor means, and an output linked to the second input of the summation means;
the filtering coefficients of the feedforward filtering means being adapted in real time according to an algorithm chosen to minimize the energy of the types of vibration which are picked up by the first sensor means as a function of the energy of the types of vibration which are picked up by the second sensor means, and of the previously measured transfer function;
which makes it possible to linearize the feedback attenuation throughout a second frequency band which is wider than the first frequency band, to accelerate the convergence of the minimization algorithm, and to enhance the robustness of the feedforward filtering means.
According to a first embodiment of the invention, the framework comprises at least one cavity bounded by an ear and passive attenuation means, the first sensor means and the actuator means being lodged in said cavity, while the second sensor means being arranged outside the cavity.
In another embodiment of the invention, the framework comprises a metal-type beam, a plate, a trellis, a seat, a ventilation duct or the like.
In practice, the first and second sensor means each comprise at least: a sound sensor element of microphone type, an acceleration sensor element of accelerometer type, a movement sensor element, a speed sensor element, a stress sensor element, a force sensor element or the like.
In one variant, the first sensor means comprise two sensor elements, one being associated with the feedforward filtering means, the other being associated with the feedback filtering means.
The actuator means preferably comprise a sound source of loudspeaker type, a test unit, a vibrating platform or the like.
The feedback filtering means advantageously comprise a plurality of active digital and/or analog filters of order greater than or equal to 1, configured to generate a transfer function making it possible to avoid instability in the first frequency band in the Nyquist sense, and the transfer function of the feedback filtering means is determined in such a way that the phase of said transfer function does not pass through the value 0 in the first frequency band.
In practice, the feedback filtering means are of the infinite impulse-response type.
For example, the feedforward filtering means are finite impulse-response filters, and the minimization algorithm is of the least mean squares type.
According to another aspect of the invention, the device comprises a plurality of first sensor means and of actuator means, and the device is centered around a structure with master/slave multiprocessors, each slave processor being tasked with driving a single actuator means.
A further subject of the present invention is a method of hybrid active attenuation of vibration, particularly of mechanical, acoustic or similar vibration, which is implemented by the device described above.